Magnetic recording systems using transducer heads that fly on an air-bearing film above magnetic recording media are well known in the art. Workers have developed and are continuing to develop such heads--for instance, enabling them to fly at a head spacing, between the transducer gap and the recording medium surface that is smaller and smaller--today, quite commonly reduced to as little as a few microinches. Such miniscule head spacing obviously complicates other problems, such as head stability (especially with a medium passing at very high speeds, and even more especially using flexible media such as floppy disks).
Also, flexible magnetic recording disks (floppy disks) are being used more and more, especially for data storage in data processing systems; such disks are relatively inexpensive compared to the more conventional rigid disk. Also it is commonly advantageous today to record on both (opposite) sides of such floppy disks as a means of optimizing the data storage capacity.
However, while transducer heads have become quite sophisticated and well developed as regards their use with rigid disks, the floppy disk recording art is considerably newer and less advanced. Many workers originally tried to employ transducer heads suitable for recording with hard disks when turning to floppy disk recording--however, as most have now discovered, this is not really possible because of the differences in the media characteristics. Such differences become magnified when there is any question of head-disk stability because of the very flexible character of the rapidly spinning floppies; and are even further exaggerated when "opposed recording" (with opposed heads on opposite side of a spinning floppy disk) is attempted, as can be imagined. This is further discussed below. This invention is intended to meet such difficulties by providing transducer head-recording-faces of a prescribed configuration especially adapted for such opposed recording with flexible media. An example of one magnetic recording head structure for such "dual sided" (not opposed) recording may be found in U.S. Pat. No. 4,074,331 to O'Reilly, et al. issued Feb. 14, 1978.
Some workers have believed that the instability of flat pivoted sliders would be cured somewhat using a convex slider face (e.g., see IBM Journal July 1959 pp 260 et seq.). However, no limits were ever appreciated (e.g., whether cylindrical or spherical; if spherical-convex, what radius limits); nor was any relation ever appreciated between spherical type faces and an "entry-taper", especially with respect to flexible media like floppy disks. Such is the thrust of this invention wherein an improved, more stable opposed-head relationship with an intermediate flexible disk is taught by using a prescribed "TSF" head-face configuration.
That is, this invention relates to an improved magnetic recording head especially adapted for dual-sided, directly-opposed, recording on flexible disks (e.g., rotated at 0-1000 rpm) having an improved "catamaran" recording face with rail faces characterized here as "tapered-spherical-flat" (TSF) air bearings. This TSF configuration will be seen to eliminate instabilities associated with conventional "flat" and "taper-flat" catamaran faces, as well as producing other advantageous features and characteristics.
Workers are familiar with the "flat air-bearing" (FIG. 1) and the "taper-flat" air bearing (FIG. 2) configurations of the (catamaran rails of) conventional known recording face configurations for non-contact recording on disk media. FIGS. 1 and 2 indicate these rather schematically. Also, a "taper-flat" configuration is indicated, for example, in U.S. Pat. No. 3,823,416 to Warner, issued July 9, 1974. This patent shows a magnetic head assembly apparently adapted for use with rigid magnetic disks, being thrust into contact therewith at times and flown over the disks at times. In this patent, a magnetic slider body is shown including three spaced "rails" with the bottom surfaces of the two outboard rails forming a "taper-flat" air-bearing surface. A magnetic core is longitudinally aligned with the center rail so as to define the transducing gap, this gap located at the "roll axis" so as to maintain the gap at substantially constant spacing from the recording surface, even during rolling motions of the assembly. Such "catamaran" structures are typically adopted to "bring one closer to the media". While they have found considerable success with rigid media, the "taper flat" catamaran faces presented grave difficulties when used with flexible media such as a floppy disk. This invention is particularly adapted to providing such "taper-flat" air-bearing surfaces with a relatively flat (very large radius) spherical (or cylindrical) surface particularly adapted for using such heads in opposed relation about a passing floppy disk in dual-sided recording.
Workers are also familiar with spherical recording faces (air-bearing surfaces) characteristic of "button" heads such as schematically indicated in FIG. 4. Such a conventional spherical head C will be understood as exhibiting a spherical recording face C-F characterized by a relatively "small radius", on the order of 2-10 inches. Head C includes a transducer insert h, positioned between a pair of conventional parallel, spaced slots S (here, insert h includes three transducer core-inserts as is known in the art). Such spherical heads are known to be relatively stable when used for recording on floppy disks (unlike a catamaran head); however, they cannot be used in "directly-opposed" relation for "dual-sided" recording, but require an opposing felt pad or the like (e.g., a resilient backing plate for single side recording). That is, as workers know, two conventional button heads cannot be used "directly opposed" for "dual-sided" recording. Their sharp curvature also shifts the read/write element away from the low-flying "tangency point" too readily. This sharp curvature (as opposed to a relatively "flat spherical" curvature with a radius of several hundred inches or more) can also interrupt flying, tending to induce a rubbing, contact with the medium. For example, using such a head with a radius of about two inches, displacing the R/W gap only about 6 mils away from tangency with the medium, will increase the flying height about 10 microinches, or 10 minutes of arc--an impossible shift for acceptable recording as workers well know. Button heads are workable only when backed up by a compliant, soft surface which can mold the passing flexible disk around the head. One can use two such button heads for "dual-side" recording, but they must be staggered and cannot be opposed because of this "back-up" requirement.
The present invention differs from these known recording face configurations in that it is characterized by a pair of catamaran rails which are not only tapered, but are "spherical-flat", rather than simply "flat"--as is illustrated for the TSF faces of the side rails of the embodiment 10 in FIGS. 3 and 5. Moreover, unlike "spherical" head-faces, this "spherical-flat" rail face is characterized by a relatively "large" radius (about 100 to 1000 inches) and hence are styled "spherical-flat" rather than simply "spherical"--as opposed to the conventional "small" (e.g., 2-10 inch) radius for spherical (non-catamaran) heads familiar to workers in this art. Such a TSF face is new in the art.
Such a "TSF" air-bearing surface will be recognized as quite advantageous as compared with conventional "flat" and "taper-flat" air-bearings, eliminating certain instabilities associated with these--and in fact represent the first genuinely stable catamaran head configuration for non-contact magnetic recording on flexible disk media.
Typical problem: "pinch-off":
FIGS. 6 and 7 are illustrative of how a pair of such TSF recording faces according to the invention operate, in "dual-side recording", with superior stability and other characteristics vs. conventional flat or taper-flat recording faces. Thus, in FIG. 6, a flexible disk segment F-D will be understood as passing, at a prescribed operating velocity, between a pair of conventional "flat" air-bearing heads A, A', each face being tilted at a prescribed divergent angle with respect to the reference plane (RF--RF) along which the disk is, ideally, to be presented. Workers will recognize that such a flexible disk will often experience undulations, as pictured, and that centering of the head pair relative to the disk may not be perfect--with the result that an undesirable "pinch-off" can occur--this intermittently closing-off, then opening-up, the "throat" (or entry inlet) between the recording faces. This will also occur with taper-flat faces. Such a "pinch-off" leads to undesirable high frequency vibrations of the disk and to unacceptable variations in flying height. These will degrade, or destroy, the desired recording performance.
With a pair of TSF recording faces according to the invention, on the other hand, as illustrated in FIG. 7, such a "pinch-off" will normally not occur at all. That is, the "taper-spherical-flat" air-bearing faces (of the catamaran rails) are observed to be considerably more stable--evidently because of the combined effects of the "entry taper" and of the spherical-flat face presented. The spherical-flat is found necessary (at least at the forward end of the rail)--along with the entry taper, to avoid "pinch-off" effects.
It is speculated that the SF faces maintain a slight Bournoulli film on (both sides) of the disk at all times. While the SF configuration is necessary along the forward half of the rail, it is also preferable to provide it relatively symmetrically along the aft end of the rail as well since an "aft SF face" appears to create a slight head/disk suction. It is noted that the very slight curvatures on such an SF face have been instrumental in eliminating "bistable" air-bearing behavior--that is, a random positioning of a head surface at two different flying heights for a given load, as mentioned above.
In any event, such a pair of TSF faces is observed to eliminate inlet "pinch-off" and permit and extremely stable air-bearing/disk spacing, as well as--most desirably--accommodating a closer head-disk spacing, with consequent improved read/write characteristics, especially at high bit densities. Similar results are observed where a single head (with back-up plate, etc.; and "single-side" recording) is likewise provided with a TSF face.
This will be surprising to workers, especially in view of the very slight curvature (large radius) placed on the "spherical-flat" rail faces.
Also surprising, it is found that such a TSF head can be made to "fly" above flexible media at "moderate" media speeds (e.g., 75-300 ips vs. the usual 1000+ips with heads on rigid disks), dropping into media contact at about 20-25 ips (for embodiment detailed here). Unlike conventional "spherical" heads, such TSF heads may be fashioned into a catamaran face and may be opposed directly about the passing media. A pair of opposed bearings that are "highly spherical", in the conventional sense (e.g., the order of a 2-10 inch radius), can in no way give such results:--in fact they are unworkable with flexible media.
And unlike the well-known flat heads used with floppy disks, the TSF head exhibits no disturbing "spacing bistability" (e.g., assuming one-unit spacing at attack angle aa; but ten unit spacing at adjacent angle bb--or "hunting" therebetween, as mentioned above).